Question

Superman is riding his bicycle. At the base of a hill, he has a specific amount of kinetic energy. Then he coasts up the hill without pedaling. He comes to a stop at the top of the hill. Why is Superman’s potential energy at the top of the hill less than his kinetic energy at the bottom of the hill?
A. The hill did work on the bicycle as he went up the hill.
B. The rest of the energy is stored in the muscles of his body.
C. He still has kinetic energy while stopped on the top of the hill.
D. Friction and air resistance created heat on his trip up the hill.

Answer 1

Answer:

D. Friction and air resistance created heat on his trip up the hill.

Explanation:

Energy transformation from one form to another is not 100% efficient. This is the postulate of the first law of thermodynamics.

Most of the energy transformation is not purely 100%.

When energy is transformed, some are usually wasted.

• In this case, in moving from bottom up, Superman produced some heat and encountered air resistance.
• To reach the top, he must have overcome the resistance and produce enough heat to power him through.
• This reduces the amount of potential energy that should have been the same as the kinetic energy down below.